The following references are believed to represent the state of the art:
U.S. Pat. No. 7,562,375 to Barrett, et al.;
U.S. Pat. No. 7,830,908 to Akgul, et al.;
US Published Patent Application 2004/223736 of Lin, et al.;
US Published Patent Application 2006/0020995 of Opie, et al.;
US Published Patent Application 2006/0083263 of Jagadeesan, et al.;
US Published Patent Application 2007/0019675 of Weber;
US Published Patent Application 2007/0248165 of Boyce, et al.; and
US Published Patent Application 2010/0111197 of Jiang, et al.